CHESTER, Pa. — Of the most regrettable parts of the Philadelphia Union’s history — and there have been quite a few regrets — the fizzling out of highly touted prospects probably ranks right near the top of the list.

Starting with Danny Mwanga in their expansion season in 2010 to their first batch of Homegrown signings to a young core that the club was supposed to build around until it didn’t, there have been several Philly players who burst onto the scene very early in their careers, only to have their development stalled and, oftentimes, their mailing addresses changed.

So when Keegan Rosenberry followed a near-perfect rookie season in 2016 with a a brutally frustrating 2017 campaign complete with benchings, injuries and even a suspension for a tweet, many Union fans couldn’t help but feel a well-here-we-go-again vibe.

But instead of continuing to spiral downward, the 24-year-old right back has enjoyed a resurgence through the first three...